Dark Side of the Moon
by uoduck
Summary: Callista Potter is living in London, turning into a werewolf each month, minding her own business. Her world is about to change dramatically when London goes crazy. Genderswapped Harry/Loki.
1. Chapter 1

AN:

I do not own either Harry Potter or Avengers or Thor.

This will be genderswap Harry/Loki.

* * *

Callista was just walking back to her home for lunch on one Wednesday morning. It looked like it was about to rain, clouds slowly moving across the sky; there was no hint of any sun from what she could see. Her wolf smelled that much even without having known the weather forecast in the muggle newspaper.

She had gotten attacked by a rogue werewolf a few years after the battle for Hogwarts. The Ministry had of course tried to get her to stay out of the public light after that since dark creatures were not liked. But with support from the public, the ministry couldn't do anything. So she stayed an auror and worked her way up to being Head of the Auror department.

She also worked up to being an alpha werewolf too. Took a lot of training and control but she did it and now she was an alpha with two pack members, one godfather and one adopted godfather.

These days, there wasn't much to do other than various clean ups of accidental muggle sightings of magic. The Death Eaters had all been captured and sentenced a couple of years ago. Frankly, Callista had grown a little bored and maybe a little... or a lot ready to find the person she would spend the rest of her life with. Her wolf was just a tiny bit picky, it seemed. It had not accepted anyone that she had seen in the past. And that was a deal breaker for her; as an alpha werewolf, both human and wolf would need to agree on someone. She had briefly dated on and off over the last few years but everyone was just a little scared of her. Though that could be that she had a pet that wasn't exactly normal, even in the wizarding world.

Regardless, she was still in London when her life would change forever. She was just a few blocks from her current apartment when she took another step and walked through a portal. She tripped and fell on a rock and cursed out loud.

"What the actual fuck!"

Callista glanced up then behind herself, belatedly seeing the... portal. It was just a circular area that was outlined in blue. She quickly scrambled up and winced when pain shot up her leg. Callista quickly looked down at her leg and pulled her wand out. A broken ankle wasn't a big deal for her so she quickly cast the spell to heal it. Then she watched as the portal closed and sighed warily.

"How the hell do I get myself in these situations? I was just minding my own business too," Callista muttered, just now realizing that she wasn't on Earth. She was in a grey world, assuming it was a world. There was...

"How can there not be colour here?"

Everything was either grey, white or black or somewhere in between those colors. As far as she could see, there were no trees or animals or just about anything. No buildings, no people, no water. It was also rather cold too and there was a breeze that was coming from nowhere. And that was when she heard a loud growling.

She turned and gaped at the sight that met her. There was a monstrous wolf behind her, chained to the ground and with a sword through its' mouth. It was about the size of one big manor and its' coat was all black. Callista tilted her head up to look it in the eyes, bringing her own wolf to the fore. The wolf had red eyes, very unusual for a wolf. Though as she wasn't on Earth so she figured she should expect anything here.

The wolf stilled, a strangled whine coming out of its' mouth due to the sword. Then Callista watched as it all but flopped to the ground, stretching its' neck and head toward her.

Callista stared for a minute, waiting, watching then hesitantly strode over to stop right before the wolf's head. The wolf looked at her like it was studying her right back, like the creature was intelligent.

"You want me to remove the sword? It looks painful," Callista murmured, reaching out her hand to rest on the wolf's cold nose. It was a bit of a reach for her but she managed. The wolf attempted to nod its' head but only succeeded in pushing the sword in further. Blood, more blood, came dribbling out of the wolf's mouth, running over what she guessed was dried blood. "Okay, hold still. I think I can do this. What kind of person would do this to a wolf? It's like someone held a really bad grudge against you."

Callista silently cast the spell that she had learned from one of her teammates and rose above the ground, hovering. The wolf was surprisingly very accommodating, holding very still and silent with an occasional huff of warm air. It wasn't even spooking at Callista floating in the air. Callista slowly floated to hover right over the bottom row of the wolf's teeth, staying still for a moment to see if this was a trap. When nothing happened except a blast of air headed toward her, she grasped the sword with both hands and tugged, adding strength that being a werewolf gave her. The wolf whined louder as the sword moved inch by inch.

"Hold on, okay? It's almost out," Callista whispered, hoping the wolf heard her reassuring tone. She tugged even harder but was careful enough to not let the sword move elsewhere in the wolf's mouth. And finally, the sword was free and Callista was almost impaled on one of the wolf's sharp teeth at a sudden movement.

"Hey, just let me get out of your mouth first? Before you do a victory dance or something," Callista muttered, quickly floating out of the gaping maw of the wolf's mouth and bringing the sword with her. Once Callista had landed back on the ground, the wolf raised itself up on its legs as far as the chains allowed it to and howled. It was a little eerie as there were no other sounds in this realm or whatever it was.

Callista watched as the wolf continued to howl for a minute or two, tail wagging happily. Or at least as well as it could, being chained to the ground also. Callista stared down at the sword in her hands and was about to fling it away when she realized that Hermione might want to study it. So she shrunk it and put it in her pack, next to various kits and things.

"I feel like I just started an apocalypse," Callista mused, staring at the wolf as it lowered itself to the ground. Its' front paws landed on the ground with a loud thud, creating a small earthquake where it was. Callista quickly rose from the ground again, rolling her eyes as the wolf howled again. "Could I come and clean up the blood near your mouth? And maybe tend to the wounds on your jaw?"

The wolf stared at her for a second then nodded, lowering its' mouth toward her. Callista floated up and over to the wolf, drawing her holly wand. She gently landed on the wolf's snout and crawled over to where the hole from the sword was. It wasn't too big but it had to be painful. She pointed her wand at the skin and fur and whispered a few spells, a numbing spell and others for healing. She pushed the fur that was in the way aside as she watched the spells go to work, feeling her magic being drawn on. As she worked, she could feel the wolf relaxing underneath her. Twenty minutes passed as she healed whatever she could find. Her stomach was by now, growling rather loudly. After all, she had missed lunch, probably.

Callista also directed her magic to the inside of the wolf's mouth, vanishing the blood and mending the spot on its' lower jaw where the sword had gone through. When she could feel that the skin and flesh were knitted together well enough, she turned to look into the wolf's eyes. She could see intelligence in there and curiosity, as well as relief.

"Can you understand me?"

The wolf's eyes twinkled a little, almost like it was saying yes.

"Well... this is new," Callista trailed off then lightly padded over to jump off from the wolf's nose, landing on the ground with a light thunk. Her dragonhide boots absorbed the impact well enough that she didn't feel anything. "Though it's not really new seeing as I talk to my snake on a regular basis. How about I attempt to get those chains off you then?"

The wolf whined excitedly and began to pant, its' mouth turning into a doggy smile.

"My name's Callista, by the way."

Callista smiled and walked around to the wolf's flank and studied the chains. They felt like magic and they were very sturdy looking chains. She wondered if her own magic would even work on them as they looked to be very old and yet new at the same time. The chains even had runes on them but they weren't... They looked like old norse or something.

"I wonder if..." Callista muttered then spoke a few words in parseltongue. The wolf stared down at her, turning its whole head to look at her.

Callista heard a noise come from the giant body next to her and turned to look the wolf in the eyes.

"I'm not going to hurt you," Callista remarked. "It's just a language that I speak."

For some reason, Callista could feel curiosity from the wolf now and...

"Wait a minute. I..." Callista trailed off, closing her eyes and having a brief conversation with the wolf inside. It was usually just images and feelings, not words but she got this message clearly enough. She opened his eyes and stared at the wolf who returned the look. "Apparently, my wolf now thinks you're part of my pack. Well that certainly escalated quickly."

Callista could now very clearly understand the surprise coming from the wolf and... hope?

"So your name is Fenrir?" Callista asked, turning back to the chains. She felt some agreement coming from the wolf as she pondered which one to cut through first. She glanced down at the chain and hissed out a word, using parselmagic. And she was immediately pushed backwards by some invisible force. Smoke rose up before her and she coughed a little.

A quiet, almost eager bark brought her attention back to her new pack mate. It had worked and one of the chains was now cut in pieces. Fenrir yipped excitedly, moving his left front paw back and forth. An almost demanding bark made Callista stand up and move to cut through the chain that was over Fenrir's other front leg. Destroying the chains took a good hour and a half and her stomach was starting to get hungry.

"Bossing an alpha werewolf around..." Callista muttered, mock glaring at Fenrir. Fenrir's excitement was contagious so much so that Callista was grinning as she worked her way through the rest of the chains.

"Alright then," Callista remarked. "You're free."

Fenrir stilled then shook like a wet dog, albeit very vigorously. The ground underneath her shook as Fenrir shook.

"You wouldn't happen to know how to get back to Earth, would you?" Callista asked, watching as Fenrir picked up one foot after another and shook them individually. "I only got here after I accidentally stepped through a peculiar portal."

Fenrir glanced at Callista then nodded his giant head, bending his legs down to crouch on the ground. Callista stared into Fenrir's eyes as the wolf picked up a paw to touch his back.

"You want me to what?!" Callista exclaimed, frowning. "You aren't a horse!"

Fenrir huffed out an irritated sounding breath and growled a little. Callista could swear that she felt what seemed like longing for a sibling from Fenrir in the next second then it vanished.

"Fine," Callista grumbled. "I'm coming."

Callista padded over to stand in between Fenrir's legs and floated up to land on the wolf's back. She gently, cautiously walked over and up to sit on Fenrir's massive head and sat down.

"Okay. I'm set," Callista muttered, frowning a little. "It's like you've adopted me."

"Or imprinted on me," Callista murmured, gaping, then crawled the rest of the way to poke her head down, staring at Fenrir upside down. "I'm not your mother!"

The wolf yipped excitedly, seeming to ignore Callista entirely.

"Or your father!"

Callista groaned then settled back down and grabbed a hold of some fur. "Okay. Let's go then."

Fenrir set off, at first just walking then trotting.

"Your legs feel okay?" Callista asked as they moved along at a fast pace. "I don't know how long you were chained down but some tingling could be expected."

Fenrir huffed but continued to trot, picking up speed. Callista could feel satisfaction coming from the wolf and decided that there was nothing to worry about, at least for right now. Though, she did think that going home with a ginormous wolf would probably cause trouble. But she would cross that bridge when she got to it. After all, they were pack mates now. She wondered how Sirius and Remus would take to having a new pack member, who was an actual wolf.

Fenrir had speeded up to what was essentially a gallop now, having gained speed very quickly. Callista cast a sticking charm on herself to ensure she stayed on. She felt the very minute that they passed through another one of those portals, the sticky glue feeling only on her for a second then they were in another realm.

"Fenrir, this isn't Earth," Callista remarked, glancing around at their surroundings. At least this realm had colour in it though it wasn't anything special. It was all black and brown, some grey. There were big rocks and caves on the horizon and it smelled like magic. And she could hear...

"There's a battle going on close by," Callista whispered and Fenrir clearly agreed, yipping a little.

Fenrir turned in the direction of where they could hear the noises and took off, sniffing the air.

"Hey, I don't think we really want to be going in the direction of a potential battle!" Callista exclaimed then sighed as Fenrir's tail started to wag. "It's not like I could really control you anyway. Plus, I'm a little curious."

If Fenrir had been human, he probably would have snickered.

"Yeah, yeah, laugh it up," Callista scolded. "I can feel your amusement. We probably are in an apocalypse. That would just be my luck though. Comment on it earlier then actually find one."

They galloped on for another fifteen minutes until they reached a small valley. Callista scanned it and her eyes caught on what looked like a small skiff. And this one looked like it could fly. Fenrir continued to run, bypassing the boat entirely and running up the mountain on the other side.

Callista gasped as they ran up it. Her wolf was starting to perk up within her mind. It was saying 'mate' continuously, over and over again.

As they reached the top of the mountain, Fenrir kicking up dirt and dust as he went along, the giant wolf stopped. They both stilled as they took in the view. There were two men and one woman down on the next valley. There were also...

"Fenrir, what are those people?" Callista whispered. "They look like... I don't know. But they're not human, that much I know."

_Dark elves. Those are dark elves, of Sv__artalfheim__. _

Callista jumped, even with the sticking charm in place, and canceled it, to move down to peer into Fenrir's eyes again.

"Was that you?" Callista asked quietly.

_Yes._

"A talking wolf," Callista muttered. "What'll they think of next?"

_I-_

"That was rhetorical," Callista grumbled.

_Oh. Did I startle you?_

"No, well, maybe a little. I should probably know better by now," Callista answered dryly."How... how can you talk?"

_I have my own magic. I got it from my father._

"Your father? So your father wasn't a wolf, I take it?" Callista asked.

_No._ _He is a sorcerer._

And with that, Fenrir howled, loudly. Callista quickly plugged her ears with her fingers and stared at the figures in the valley. They all stopped, turned around and stared.

Callista stared too as her wolf was all but drowning her mind in MATE! She drew on her wolf to enhance her vision and scanned the people down there, bypassing the woman and the guy with the hammer to land on the guy with green armor. MATE!


	2. Chapter 2

Loki stared and stared at his son. Fenrir was at the top of the cliff and was staring intently back at him, a wide wolfish grin on his face. Well... This was unexpected.

"Loki, is that.." Thor trailed off, distractedly hitting a dark elf with Mjolnir.

"Yes, that is Fenrir," Loki replied, knifing another dark elf as one attempted to stab him.

Thor turned to glare at him. "Was this part of your plans? Were you going to betray me by turning Fenrir on me? My nephew?"

Loki sighed. "How would I be able to do that? I was in prison for however long I was. I'm certainly not telepathic."

"Uh, guys," Jane broke in. "Firstly, your son? Secondly, Thor, um, a little help here."

Loki turned to look at Jane, who was being stalked by the Kurse. Thor immediately raced over to put himself between Jane and the creature. The ground trembled as Kurse prowled closer to Thor but then as they heard another howl, Loki figured that the ground was half trembling due to Kurse and half due to Fenrir running down hill towards them. And that was when he realized that there was a woman sitting on his son's head.

Loki stared, refusing to show any emotion here with Thor and his mortal for company. There was a woman on top of Fenrir, riding him like a horse. And Fenrir hadn't as of yet made any attempt to throw the woman off.

The minute that Fenrir reached them, the giant wolf padded over to where Thor and Kurse were fighting, dropped his head down and squeezed his big jaws around Kurse. The creature screamed; the scream was abruptly cut off as Loki watched Fenrir's jaws close over the creature, tightening more and more until the distinct sound of spinal breakage and neck breakage was heard.

"Fenrir, why... I so did not want to see that," the woman on top of Fenrir remarked. "I've had my share of seeing nasty things but that takes the cake. I'm getting off this ride."

Fenrir whined low in his throat then with a great heave, pitched Kurse far, far away. The woman grimaced but sighed and turned to stare at Loki again. The woman was clothed in strange wear; it was clearly armor of some sort but it didn't look like any kind of armor Loki had seen. Out of the corner of his eyes, Loki could see that Thor and Jane were staring at both the wolf and the woman.

"Alright, I'm coming down. No, you don't need to kneel. I can float down."

The three of them watched as the woman stood up, walked over to the edge of Fenrir's back and... hovered in the air for a second before floating down.

"She's a sorcerer," Thor remarked excitedly. "She's like you, brother."

"Thanks. I hadn't noticed," Loki replied dryly.

Once the woman was on the ground, she strode over stand in front of them. Loki stared at the woman, looking her over before focusing on her eyes. They were green, with a hint of...

"I'm Callista Potter," the woman held out her hand to Jane first.

"Jane Foster." Jane held out her own hand hesitantly. "What... how..."

Callista chuckled. "And you two would be... who?"

Jane's eyes widened. "You don't know who these two are? You are from Earth right?"

"Yes, aren't you?" Callista asked, looking between Jane, Thor and Loki with a puzzled frown.

Loki for once was speechless as he watched Fenrir lower his head and headbutt Callista gently. Callista smiled and reached her hand to ruffle Fenrir's fur.

"He likes you," Loki remarked.

Callista turned to stare at him, raising an eyebrow. "You're his father, right?"

"Yes..."

Loki turned to look into Fenrir's eyes, seeing amusement in them and happiness. He strode over to stand in front of his son and held out his hand.

"Fenrir..."

Fenrir yipped and sniffed him for a second before padding over to headbutt him. Loki dimly heard Callista chuckle.

"To belatedly answer your question," Callista started. "Yes, I'm from Earth. I just don't know who your friends are."

"My son," Loki whispered, bringing a hand to curl into Fenrir's fur and lowering his head to touch Fenrir. "How... how did you escape?"

_This mortal human helped me._

"She helped you?" Loki asked. "But she's just a human sorcerer. I was not aware that there were sorcerers on Midgard."

"Midgard?"

Loki withdrew from Fenrir to glance at Callista.

"Where the hell are you guys from?" Callista asked, looking between Thor and Loki. Loki watched as she ran a hand through her light auburn hair and noticed the peculiar scar on her forehead. It was shaped like the lightening bolts that were often associated with Thor's thunder.

"I am Thor, of Asgard. Son of the Alfather."

Callista looked dubiously at Thor. "Asgard? Well, I suppose after the day I've had, I can accept that there are other realms. Where are you from then?"

Loki started. "I am Loki, of Jötunheim."

Loki saw Thor wince and smirked. He turned to glance at the human only to see her mutter something under her breath. Something about a mate? That must be a Midgardian term, one that he wasn't aware of the meaning.

"You're saying that you don't know about him?" Jane asked, jerking a thumb in Loki's direction.

Callista turned to look at Jane then at Loki then shook her head. "Um, should I?"

Jane gaped. "Last May? New York?"

"That fuss in the mu- in New York that everyone was talking about?" Callista asked then frowned. "Yeah, I was really, super, busy that month. There was something that my department couldn't handle without me. I was in Australia around that time."

Loki stared at the human, narrowing his eyes. The mortal had been about to say something.

"Jane," Thor started, clearing his throat. "Did you see anything when the Aether transferred?"

"Oh, yeah," Jane exclaimed, eyes narrowing in worry. "Malekeith is going to use it."

"The Aether?" Callista asked, staring at the three of them then Loki watched as she turned to Fenrir. "Oh, so this is an apocalypse. You brought me into this, you know."

Fenrir chuffed.

"Fine. I'll help them. If only to-"

"Is my son talking to you?" Loki asked.

Callista turned to look at Loki and nodded. "He's talking to me. He only started right when we saw you guys though. I think his chains were dampening his magic."

Loki nodded thoughtfully. "Likely. How did you break them then?"

"I used what I had," Callista replied, shrugging a little.

Loki raised an eyebrow. "I was under the impression that just magic wouldn't work."

"It probably wouldn't," Callista remarked, still staring straight at Loki who was beginning to be a little unnerved at the stranger's attention. "I used some ancient magic though and it worked."

"Ancient?"

"Yeah, the magic of snakes?" Callista offered. "I can speak their language so..."

Loki stared. "A mortal who can speak the language of snakes. I'm... I hesitate to say this but I am impressed."

_If you two are done flirting, I am in need of food._

Callista immediately blushed, rocking back on the heels of her feet. "Fenrir! That's not- We're not-"

Loki stared at the midgardian then at his son. "Of course. However, Svartalfheim does not have any animal life to speak of."

"When we get back to Earth," Callista started, turning to look at Fenrir. "I can have someone get some meat for you, assuming you want meat that is."

_Yes, that would be good._

"So, about getting back to Earth," Jane said, looking between Callista, Loki and Fenrir. "How are we going to do that?"

Thor turned to look at their surroundings. "I do not see any portals that would lead back to Midgard."

"So, what's the deal then?" Callista asked, staring between Jane, Thor and Loki. Out of the corner of his eyes, he watched as Fenrir took a step or two closer to Thor and sniffed him. Thor smiled and stroked Fenrir's fur after attaching Mjolnir to his waist. "What kind of apocalypse is this?"

"The leader of the dark elves wants to use the Aether to destroy the world," Jane replied, glancing around at their surroundings.

"To bring darkness to it," Loki remarked. "That's what he wants to do. He doesn't actually want to destroy it."

Callista quirked an eyebrow. "Bring darkness to the world? That sounds rather ominous, I suppose."

"It would destroy the world," Jane commented. "That's why we need to get back home."

"See, Fenrir," Callista said, throwing up her hands and turning to stare reproachfully at Fenrir. "That's what I was trying to do. Though I guess if you guys are telling the truth and all, Earth has a different name for you?"

"Yes, we call it Midgard," Thor replied, pulling away from... his nephew.

"Quickly would be good, I think," Thor added, looking beyond their little group. Callista turned to see a fast approaching dust storm and flinched. She scanned the horizon, looking for a place to shelter and spotted a cave.

"Ah, there!" Callista exclaimed, pointing to it. "We can plan there without getting choked to death by sand."

Jane grimaced and nodded. "Sounds good. Let's go."


End file.
